Multiple myeloma (MM) is one of the most common hematological neoplasms, constituting about 1% of all human cancers and 2% of all cancer deaths. MM is preceded by monoclonal gammopathy of undetermined significance (MGUS), one of the most common pre-cancerous conditions afflicting 3% of the United States population over 50 years old. Although MM is regarded as an environmental disease, it is not yet clear what promotes the progression from MGUS to the deadly MM. One of the unique features of MM is the extremely low mutation rate of the tumor suppressor p53 gene. Genomic instability (chromosome translocation, aneuploidy, and gene mutation) is widely observed in MM cases, suggesting that the function of p53 as the guardian of the human genome is compromised. We previously analyzed the molecular mechanisms of p53 inactivation in MM cells by a new class of noncoding small RNAs, microRNAs (miRNAs). Data from our laboratory and others have shown that multiple miRNAs suppress expression of the human p53 gene and that a majority of these miRNAs are overexpressed in MM. We hypothesize that the ubiquitous environmental pollutants benzo[a]pyrene (BaP) and tetrachlorodibenzodioxin (TCDD) disrupt functional interactions of miRNA:p53 to mediate p53 inactivation over the course of MM. In this renewal application, we propose 3 specific aims to advance our investigations into the molecular etiology of MM and identify potential treatment and preventive strategies. In Aim 1, we will dissect the underlying mechanisms of upregulation of miRNAs in MM cells exposed to BaP and TCDD. In Aim 2, we will determine, using murine syngeneic xenograft and genetic models, whether BaP directly promotes MM progression via one miRNA gene cluster that targets p53. In Aim 3, we will determine whether epigallocatechin gallate (EGCG, the main component in the botanical drug Polyphenon(R) E) prevents or inhibits MM progression induced by BaP or TCDD. Completion of the goals in this proposal will reveal the role of environmental hydrocarbons in p53:miRNA interaction and in MM etiology and provide a repurposed drug for MM prevention and therapeutic intervention.